IEEE 1588 has been proposed as a technique for synchronizing the times of certain devices on a network with less than one microsecond precision. For example, the synchronization method based on IEEE 1588 is implemented by a grandmaster-mode device coupled to a precise time source such as a GPS (Global Positioning System) satellite, a standard radio wave, an atomic clock or the like; a boundary-clock-mode device that relays time information transmitted from the grandmaster-mode device; and an ordinary-clock-mode device in which the time information transmitted from the boundary clock mode is terminated.
The grandmaster-mode device receives TOD (time of day) and PPS (pulse per second) information from a precise time source such as a GPS satellite to synchronize the time of the grandmaster-mode device. The boundary-clock-mode and ordinary-clock-mode devices use PTP (precision time protocol) to send PTP packets to ask the grandmaster-mode device the time at an arbitrary timing.
The grandmaster-mode device receives the PTP packet used to request the time. The grandmaster-mode device sends a time notification PTP packet that includes the TOD and PPS information to the boundary-clock-mode device and the ordinary-clock-mode device that sent the PTP packets requesting the time, after stamping the transmission time on the time notification PTP packet.
The boundary-clock-mode device and the ordinary-clock-mode device use a timestamp of the time when sending the PTP packet requesting the time and the timestamp of the time notification PTP packet to calculate a delay time in the transmission path. The boundary-clock-mode device and the ordinary-clock-mode device synchronize the times thereof by correcting the times with respect to the time of the time notification PTP packet sent by the grandmaster-mode device based on the delay time.
Japanese Laid-open Patent Publication No. 7-287083A, for example, is disclosed as a related art document relating to the above technology.